The hallmark of the immune response seen in individuals with patent lymphatic filariasis is a profound inability to proliferate or produce cytokines associated with a Type 1 response (IL 2 and IFN &#947;) in response to parasite antigen. This parasite specific anergy is mediated, in large part, by IL 10 with TGF &#946; and CTLA-4 playing smaller regulatory roles. Other members of the IL-10 superfamily (IL-19 and IL-24) have been now shown to be upregulated in patent LF, a process driven by IL-10 itself. The mechanisms underlying the modulation of parasite-specific responses in LF continues to be a major research question. Using multiparameter flow cytometry, this antigen-specific modulation was shown to be associated with an expansion of IL-10 producing adaptive Treg and altered development of parasite-specific central and effector memory T cell populations 4. We have demonstrated that these Tregs influence both effector T cells and antigen presenting cells (APCs), but alter APC function indirectly through the effector T cells (Metenou et al, submitted). Most recently, we have identified, using protein expression profiling (by LC/MS/MS) of nTregs in the context of filarial infection, 2 additional molecules (WISP3 and PSG-1) that are secreted by nTregs that suppress T cell proliferation and IFN&#8722;&#947; production by effector T cells in a contact independent manner. Not only has patent filarial infection been shown to modulate T cell responses, but it has also been shown to result in profound monocyte dysfunction (review here) that can be reversed by effective treatment with anti-filarial chemotherapy. Subsequently we have shown that LF induces an immunoregulatory population of monocytes that appear to be human parallels of alternatively activated macrophages. In addition, LF is associated with an expansion of CCR1 low circulating myeloid DCs 6 suggesting the myeloid populations may be of great import in the modulation of filarial-specific T cell function. Expansion of a non-classical (CD16hi) monocyte subset has very recently been identified in LF. Moreover, we have shown that in human monocytes populations the major 2 subsets (CD14+CD16- and CD14+CD16lo) have a clearly differential response to microfilariae (Mf) 7, the latter preferentially producing the regulatory cytokine IL-10. Using human monocyte derived dendritic cells (DC), we have explored the mechanisms by which parasite products alter the function of human APCs. Having previously shown that mf-derived soluble products interfere directly with TLR3 and TLR4 signaling pathways, we were next able to demonstrate that parasite products profoundly modulated the DCs ability to produce IL-12, CCL10 and CCL11 8 in response to antigen or TLR agonists. By using approaches to silence important transcription factors, we were able to demonstrate the parasite-induced diminution of IRF-1 in DCs dramatically alters IL-12 production thereby preventing INF-&#947; (and other Th1-associated) responses in LF 9. Moreover, using global protein expression profiling comparisons between Mf-exposed or unexposed human mDCs, mf significantly downregulated the mammalian target of rapamycin (mTOR) and the eukaryotic initiation factor (eIF) 2, eIF4 and p70S6K. Interestingly, live mf produce and secrete homologues of human FKBP1 (cyclophilin) a negative regulator of mTOR signaling. The effect of chronicity of infection per se on the T cell response to filarial infection has been studied by an exhaustive comparison of gene expression between cells purified from those with lifelong filarial infection and those expatriates with relatively acute infection. Using gene expression profiling, we were able to show that longstanding filarial infection (based on global gene expression ex vivo) showed a markedly down-regulated pattern of gene expression most notably in CD8+ cells but also in CD4+cells/ In a study that has taken advantage of cells cryopreserved from well characterized individuals from the Cook Islands where W. bancrofti is endemic, we have utilized multiparameter flow to demonstrate not only a diminished number of central memory cells (CD4+CCR7+CD127+CD27+CD45RA-) in chronically infected patients but also an increase number of revertant memory cells (CD3+ CD45RA+CCR7-CD127+CD122+) suggesting that chronicity in helminth infection (like in chronic viral infection) may predispose to memory cell dysfunction. Because chronic filarial (and other helminth) infections may alter immune reactivity to other (non-parasite) antigens and because these alterations may have profound implications for the clinical outcome of these non-filarial infections, collaborative studies in India, Mali, and Ecuador have shown that the presence of active filarial infection and/or chronic intestinal helminth infection very clearly blunts the Type 1 (and Th17) response to non-filarial antigens in the context of co-infection. Over the past four years, we have focused on the influence of pre-existing helminth infections on Mycobacterium tuberculosis (Mtb), malaria, and HIV. As a first step in examining the interaction between Mtb and filarial infection and based on the epidemiology of filarial/Mtb coinfection, an in vitro system of co infection was established and used to demonstrate that pre-exposure of human DCs and macrophages to live filarial parasites induces immunoregulatory phenotypes that alters mycobacterial entry and replication (Chatterjee, unpublished). Concurrently, we developed an in vivo model in which we rendered mice microfilaremic and then infected them (by aerosol) with virulent Mtb. Our data very clearly suggests that microfilaremia induces alternative activation of macrophages in the lung but fails to alter the growth or clearance of Mtb; microarray data from the lungs of these mice suggest a generalized modulation of interferon-gamma and IFN-&#947; regulated pathways (Chatterjee, Talaat, unpublished). Human studies ex vivo focusing more on latent tuberculosis in filarial-infected and -uninfected individuals have demonstrated that filarial infections: 1) modulate TLR expression and function in response to Mtb antigens 12; 2) markedly alter the Mtb-specific Th1/Th17 responses so important in maintaining latency through the concerted actions of CTLA-4 and PD-1 2; and 3) induce a population of Tregs that modulate Th17 responses in patients with latent Mtb infection 13. We have now extended these studies by developing multiparameter flow cytometric approaches to identify Mtb-specific stem cell memory (SCM) CD4+ and CD8+ T cells and are exploring the relationship between chronic filarial antigen exposure and the alteration in Mtb-specific memory In studies in Mali that have combined clinical and immunological aspects of malaria and filarial co-infection, our immunologically-focused studies have explored the bystander effects of pre-existing filarial infections on the response to malarial antigens longitudinally (before, during, and following the malarial transmission season). In two studies performed in different sites two years apart, we have shown quite conclusively that the presence of filarial infection modulates the innate (TLR-mediated) response to malarial antigens; more importantly, however, we have shown that filarial infection modulates malaria-specific Type 1 cytokine responses in an IL-10 dependent manner in a filaria/malaria co-infected population. We have identified the cell populations regulating the malaria-specific pro-inflammatory cytokine pathways in the co-filarial/malaria co-infected populations, and we have also demonstrated that filarial infections prevent almost completely the induction of malaria-specific polyfunctional T cells. Furthermore, we have demonstrated the pivotal role played by IRF-1 in the modulation of the malaria-specific Th1/Th17 responses.